1. Field of the Invention
The present invention relates to an electron beam generator device for emitting electron beams, such as electron source of electron microscope (filament of electron gun) and cathode electrode of FED (field-emission display), and to a method for producing it. In particular, the invention relates to such an electron beam generator with carbon nanotubes and to a method for producing it.
2. Description of the Related Art
As having a unique structure and unusual characteristics, carbon nanotubes (CNT) may have various applications. Carbon nanotubes have a cylindrical shape of one-dimensionality formed by coiling up a graphene sheet of carbon hexagons. Those having a structure of one graphene sheet are referred to as single-walled nanotubes (SWNT), and those having a structure of multiple graphene sheets are referred to as multi-walled nanotubes (MWNT). SWNT have a diameter of about 1 nm, and MWNT have a diameter of a few nm or so; and they are extremely thin as compared with conventional carbon fibers.
Carbon nanotubes have a length of an order of micrometers, and are characterized in that the aspect ratio thereof to diameter is extremely large. In addition, carbon nanotubes have a spiral structure of carbon hexagons, and therefore have extremely unusual characteristics in that they have both properties of metal and semiconductor. Moreover, the electroconductivity of carbon nanotubes is extremely high, and they may conduct a current of at least 100 MA/cm2 in terms of the current density through them.
Not only such electric characteristics, carbon nanotubes have many excellent mechanical properties. Specifically, since they are made up of carbon atoms only, they are extremely lightweight but have a Young's modulus of over 1 TPa and are extremely tough. In addition, since they are a cage substance, they have good elasticity and stability. To that effect, carbon nanotubes have various excellent properties and are extremely attractive substances as industrial materials.
Various application studies based on the excellent characteristics of carbon nanotubes have heretofore been made. Carbon nanotubes are added for resin reinforcement or for producing conductive composite materials, and they are used for probes of scanning probe microscopes. In addition, carbon nanotubes are utilized as micro electron sources for field-emission rectifier devices and flat displays, and are being applied to hydrogen storage.
Further, since carbon nanotubes have an extremely large aspect ratio as so mentioned hereinabove, and their edges are sharp, and, in addition, they are chemically stable and mechanically tough. Accordingly, they are promising emitter materials for field-emission technology. Heretofore, many studies for practicability of field-emission electron devices and flat displays with carbon nanotubes have been made.
In the document (Niels de Jonge, Yann Lamy, Loen Schoots & Tjek H. Oosterkamp's “High Brightness Electron Beam from a Multi-walled Carbon Nanotube” in Nature, Vol. 420, pp. 393-395, 2002), it is disclosed that a technique of utilizing carbon nanotubes as an electron source of electron microscopes, as a type of microelectron sources. The electron source (electron gun) of electron microscopes heretofore known in the art includes thermal emission devices with tungsten V-shaped filament or LaB6 chip therein, and field-emission devices with tungsten single-crystal chip therein. In general, the brightness of field-emission devices is high and the energy width thereof is small, and therefore field-emission devices are favorable for the electron source of electron microscopes. The electron source disclosed in the document comprises carbon nanotubes fixed on tungsten chips, and it emits electron beams in a mode of field emission. It is known that the brightness of the electron beams from it, actually measured, is larger by at least 10 times than that from conventional devices.
However, the method of producing the electron source disclosed in the document comprises using a piezomanipulator in a scanning electron microscope to pick up one or a few carbon nanotubes and fixing them to a tungsten chip therein. The method is advantageous in that suitable carbon nanotubes may be selected in any desired manner, but it takes a lot of time and labor for producing the intended product and its productibity is extremely low.